1. Field of the Invention
The present invention relates to a vehicle such as a riding lawn mower, provided with a transaxle apparatus supporting an axle to which wheels are attached. More particularly, it relates to a structure of the transaxle apparatus, and a structure for drivingly connecting front and rear transaxle apparatuses in the vehicle to each other.
2. Related Art
Conventionally, there is a well-known articulate riding lawn mower with a pivotally connected first frame and second frame so as to allow the second frame to be folded relative to the first frame. The first frame is equipped with an engine and a transaxle apparatus supporting an axle driven by the engine. The second frame is equipped with a working device such as a mower device, a driver""s unit, and an axle casing supporting a freely rotatable axle. Furthermore, a riding lawn mower provided with an Ackerman type steering system is also well known.
For example, the Japanese Patent Laid Open Gazette 2000-270,651 discloses an articulate four-wheeled lawn mower in which the first frame serves as a rear frame and the second frame serves as a front frame. The rear frame is provided with an HST (a hydrostatic transmission) for transmitting engine power to rear wheels supported by the rear frame. Also, the rear frame is provided with a power take-off shaft for taking out power from a pump shaft of a hydraulic pump of the HST so as to transmit the rotation of the power take-off shaft to a mower device supported by the front frame.
The vehicle of such conventional structure is a so called two-wheel drive vehicle, wherein, while the axle supported by the first frame usually disposed rearward is driven by the engine, the axle supported by the axle casing of the second frame usually disposed forward idles regardless of the power for driving the axle of the first frame.
However, the two-wheel drive vehicle, which drives only rear wheels, is disadvantageous in gradeability on a slope and roadability on a bad road. The vehicle, when being bogged in mud etc., cannot escape easily. Thus, in order to resolve the problem, the vehicle is desirably made into a four-wheel drive type, which drives both rear and front wheels.
As a conceivable manner for solving the problem, a four-wheel drive articulate vehicle may be provided. However, in the above-disclosed vehicle including the rear frame on which the engine and the power take-off shaft are mounted, the power take-off shaft is rotated synchronously to rotation of the pump shaft so that the rotary speed of the power take-off shaft is constant as long as the rotary speed of the engine is constant, while the rotary speed of the rear wheels driven by output of the hydraulic motor is changed by speed change operation for adjusting a swash plate angle of the hydraulic pump. Thus, the power take-off shaft for driving the working device cannot be used as a front-wheel drive shaft simply. Even if another power take-off shaft is allowed to be provided in the transaxle apparatus on the rear frame so as to take out output power of the HST and to drive the front wheels synchronously to the rear wheels, there is considerable limitation in arrangement of a mechanical transmission system between the transaxle apparatuses on the front and rear frames because it is necessary to ensure the rotatability of both the frames and to arrange the transmission system for driving the working device in the place. The four-wheel drive articulate vehicle disclosed by U.S. Pat. No. 6,425,452, in which both the transaxle apparatuses on the respective first and second frames incorporate respective HSTs, is very expensive and requires both the HSTs to be controlled synchronously.
An object of the invention is to provide a four-wheel drive vehicle with high flexibility of parts arrangement depending upon hydraulic piping serving as transmission means between front and rear transaxle apparatuses.
To achieve the object, a vehicle according to the invention comprises a first transaxle apparatus disposed at one of front and rear portions of the vehicle, a first axle supported by the first transaxle apparatus, a first hydraulic motor for driving the first axle integrally assembled in the first transaxle apparatus, a second transaxle apparatus at the other of front and rear portions of the vehicle, a second axle supported by the second transaxle apparatus, a second hydraulic motor for driving the second axle integrally assembled in the second transaxle apparatus, and a common variable displacement hydraulic pump drivingly connected to an engine and fluidly connected to the first and second hydraulic motors.
Preferably, the vehicle is a riding lawn mower.
Preferably, the first hydraulic motor of the first transaxle apparatus and the second hydraulic motor of the second transaxle apparatus are fluidly connected to the common hydraulic pump in series.
Preferably, a pair of axles serve as the first axle of the first transaxle apparatus and are differentially connected to each other through a differential gearing, and another pair of axles serve as the second axle of the second transaxle apparatus and are differentially connected to each other through another differential gearing.
Preferably, a differential-lock system is provided in each of the differential gearings so as to cancel the differential rotation of the pair of first axles or of the pair of second axles.
Preferably, a switching valve is interposed on a connection way between the common hydraulic pump and the first hydraulic motor of the first transaxle apparatus so as to control the supply of fluid to the first hydraulic motor.
Preferably, a fluid sump in the first transaxle apparatus, a fluid sump in a second transaxle apparatus, and a fluid sump in the common hydraulic pump are fluidly connected to one another so that hydraulic fluid is circulated among the fluid sumps.
The hydraulic motor is required to prevent output force thereof transmitted to each of the hydraulic motors from being reduced and to constitute a drive train with the corresponding transaxle apparatus compactly.
Then, as an aspect, the hydraulic motors are incorporated in the respective first and second transaxle apparatuses.
In application of a four-wheel drive system to the vehicle, it is desirable to achieve standardization of manufacture parts so as to save the manufacturing costs.
Accordingly, the first and second transaxle apparatuses are identical with each other in structure.
In application of the four-wheel drive system, necessary transmission means for transmitting power to a working device, which is needed in the conventional vehicle, must be modified.
Therefore, a pair of axles serving as the second axle supported by the second transaxle apparatus are different in length from each other, and a transmission element for drivingly connecting the engine to the working device crosses a longer axle of the pair of second axles.
In arrangement of the first and second transaxle apparatuses, it is necessary to consider weight balance of the vehicle.
Consequently, the first and second transaxle apparatuses are identical with each other in shape, and distributed into one side and the other in a lateral direction of the vehicle.